Adamantane has a structure in which four cyclohexane rings are bound to one another in a cage fashion, and is a compound having high symmetry and stability. Also, adamantane exhibits a specific function. Accordingly, adamantane is known to be useful as, for example, a lubricant, a starting material for an agricultural chemical or for a drug, or a starting material for a high functionally industrial material because adamantane shows a specific function.
Adamantane is obtained by isomerizing trimethylenenorbornane (TMN), which is obtained by hydrogenating dicyclopentadiene (DCPD), by using a catalyst. In addition, aluminum chloride is industrially used as the catalyst.
In addition, a known example of a solid catalyst is one obtained by causing zeolite subjected to cation exchange to carry an active metal such as platinum, rhenium, nickel, or cobalt by means of an impregnation method (see, for example, Patent Document 1).
When adamantane is produced by using aluminum chloride as a catalyst, in addition a large amount of the catalyst must be used, the catalyst cannot be recycled because the catalyst forms a complex with a heavy component during a reaction. Therefore, when the method is employed, a large amount of waste aluminum is produced. The disposal of waste aluminum is responsible for the problem of environmental pollution.
Furthermore, when aluminum chloride is used, there arises the following problem: produced adamantane is colored, so a decolorization step by using recrystallization, activated carbon, and the like is needed, and hence a subsequent treatment step vexatiously becomes complicated.
On the other hand, a process for producing adamantane involving the use of a catalyst obtained by causing zeolite subjected to cation exchange to carry an active metal such as platinum, rhenium, nickel, or cobalt by means of an impregnation method results in a low yield unless hydrogen chloride is made to coexist (TMN conversion ratio of 79.5%, adamantane selectivity of 10.1%, adamantane yield of 8.0%). Therefore, hydrogen chloride is indispensable to the process, and hence the process involves, for example, a problem in that an expensive device made of a corrosion-resistant material must be used owing to the strong corrosivity of hydrogen chloride.
In view of the foregoing, the inventors of the present invention have made studies with a view to coping with the above-mentioned problem, and have found an effective process for producing adamantane involving the use of not hydrogen chloride but a metal-carrying solid acid catalyst. In the process, an isomerization catalyst and how to use the catalyst in a reaction field have been proposed, but no industrial technique for producing adamantane including separation and purification treatments for produced adamantane has been disclosed.
Patent Document 1: JP-B-52-2906